Kyung Hee University · Physics and Astronomy
Professor Evgenij Zubko's research lab specializes in computational electromagnetic scattering and polarimetry of complex, irregularly shaped particles relevant to astrophysical and planetary science. The lab focuses on developing and validating numerical methods—such as the discrete dipole approximation (DDA) and superposition T-matrix method—for modeling light scattering by agglomerated, porous, and fractal-like dust particles. Key research directions include understanding the photopolarimetric signatures of cometary dust, interpreting in situ measurements from space missions (e.g., Stardust), and refining models of interplanetary and cometary dust morphology and composition. The lab also investigates the limitations and accuracy of scattering theories under various physical conditions, particularly for particles with high aspect ratios or strong absorption.
Figures are computed from collected data and may differ slightly.
We consider electromagnetic scattering by a spherical volume sparsely and randomly populated by spherical particles of equal size and optical properties. The far-field scattering matrix of the entire volume is computed using an exact method and an approximate method. The former is a direct computer solver of the Maxwell equations called the superposition T-matrix method (STMM). The latter is a solver based on numerical Monte Carlo integration of the ladder and cyclical diagrams appearing in the
There are two widely accepted restrictions on the application of the discrete dipole approximation (DDA) in the study of light scattering by particles comparable to the wavelength: (1) when considering dielectric particles, the size of the cells must satisfy the condition kd|m|<0.5, where k is the wavenumber, d is the size of the cells, and m is the complex refractive index of the constituent material and (2) when considering conductive particles, the size of the cells must be small enough to re
We used the discrete dipole approximation to study the backscattering of agglomerate particles consisting of oblong monomers. We varied the aspect ratio of the monomers from approximately 1 (sphere) to 4, while we kept the total particle volume equivalent to that of an x = 10 sphere for m = 1.59 + i0 and 1.50 + i0 and considered two values of agglomerate packing density: rho = 0.25 and rho = 0.1. We found that these particles do not display a prominent brightness opposition effect but do produce
The low abundance of refractory carbonaceous material in samples collected by Stardust in comet 81P/Wild 2 coma was completely unexpected. If these results are universal to other comets, this necessitates a reformulation of current models of solar system formation. A polarimetric imaging analysis demonstrates that dust is not uniformly distributed within cometary coma, and that the circumnucleus halo region where the dust samples were collected must contain a low population of carbonaceous parti
We analyse the photopolarimetric response measured in Comet C/1975 V1 (West) using model agglomerated debris particles. Such particles have highly irregular morphology and volume density with properties that are consistent with the samples retrieved by Stardust from Comet 81P/Wild 2. We find that an entire set of observational data including phase function, phase dependence of the degree of linear polarization, photometric, and polarimetric colour in Comet C/1975 V1 (West) can be quantitatively
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